TRANSPORT-THEORETIC MODEL FOR THE ELECTRON-PROTON-HYDROGEN ATOM AURORA .1. THEORY

The first self-consistent transport-theoretic model for the combined e lectron-proton-hydrogen atom aurora is presented. This is needed for a ccurate modeling of the diffuse aurora, particularly in the midnight s ector, for which a statistical study (Hardy et al., 1989) indicates th at the proton contribution to the total auroral energy flux is (on the average) about 20 to 25% of that of the electrons. As a result, the i onization yield as well as the yields of many emission features will b e underestimated (on the average) by about the same percentage if the proton-hydrogen atom contributions are neglected. The model presented here can also be used to study a pure electron aurora or a pure proton -hydrogen atom aurora by choosing the appropriate boundary conditions, namely, by setting the incident flux of one or the other particle pop ulation equal to zero. In the latter case, the new feature of the pres ent model is the rigorous transport-theoretic treatment of the contrib utions to ionization rates and to emission rates and yields from the s econdary electrons produced by protons and hydrogen atoms. A coupled s et of three linear transport equations is presented. Protons and hydro gen atoms are coupled only to each other through charge-changing (char ge exchange and stripping) collisions, while the electrons are coupled to both protons and hydrogen atoms through the secondary electrons th at they produce. Source functions for the secondary electrons produced by the three primary particle populations are compared and contrasted , and the numerical methods for solving the coupled transport equation s are described. Finally, formulas for calculating pertinent aurora-re lated quantities from the particle fluxes are given. In the companion paper (Strickland et al., this issue), the model results are presented .